8-speed transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets having six torque-transmitting devices, two fixed interconnections and a grounded member. The powertrain includes an engine and torque converter that is continuously connected to at least one of the planetary gear members, and an output member that is continuously connected with another one of the planetary gear members. The six torque-transmitting devices provide interconnections between various gear members, and the transmission housing, and are operated in combinations to establish at least eight forward speed ratios and at least one reverse speed ratio.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 60/910,009, filed Apr. 4, 2007 and which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a power transmission having threeplanetary gear sets that are controlled by six torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five- or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

The preferred embodiment of the present invention provides an improvedtransmission having three planetary gear sets controlled to provide atleast eight forward speed ratios and at least one reverse speed ratio.

The transmission family of the present invention has three planetarygear sets, each of which includes a first, second and third member,which members may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order.

In referring to the first, second and third gear sets in thisdescription and in the claims, these sets may be counted “first” to“third” in any order in the drawings (i.e., left to right, right toleft, etc.). Additionally, the first, second or third members of eachgear set may be counted “first” to “third” in any order in the drawings(i.e., top to bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a sing-pinion carrier member (simple)or a double-pinion carrier member (compound). Embodiments with longpinions are also possible

A first interconnecting member continuously connects the sun gear memberof the second planetary gear set with the sun gear member of the thirdplanetary gear set.

A second interconnecting member continuously connects the planet carrierassembly member of the second planetary gear set with the planet carrierassembly member of the third planetary gear set.

The planet carrier assembly member of the first planetary gear set iscontinuously connected with a stationary member (transmissionhousing/casing).

The input member is continuously connected with the sun gear member ofthe first planetary gear set. The output member is continuouslyconnected with the ring gear member of the third planetary gear set.

A first torque-transmitting device, such as a brake, selectivelyconnects the sun gear member of the second planetary gear set with astationary member (transmission housing/casing).

A second torque-transmitting device, such as a brake, selectivelyconnects the planet carrier assembly member of the second planetary gearset with a stationary member (transmission housing/casing).

A third torque-transmitting device, such as a clutch, selectivelyconnects the sun gear member of the first planetary gear set with thesun gear member of the second planetary gear set.

A fourth torque-transmitting device, such as a clutch, selectivelyconnects the sun gear member of the first planetary gear set with theplanet carrier assembly member of the second planetary gear set.

A fifth torque-transmitting device, such as a clutch, selectivelyconnects the ring gear member of the first planetary gear set with thering gear member of the second planetary gear set.

A sixth torque-transmitting device, such as a clutch, selectivelyconnects the ring gear member of the first planetary gear set with thesun gear member of the second planetary gear set.

The six torque-transmitting devices are selectively engageable incombinations of two to yield at least eight forward speed ratios and atleast one reverse speed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets. The transmissionis particularly useful in a front-wheel drive configuration. Also, ituses all single transition shifts, and provides two overdrive ratios.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is a schematic representation of the powertrain of FIG. 1 adepicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes three planetary gear sets20, 30 and 40.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 124, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27, 28 rotatablymounted on a carrier member 29. The pinion gears 27

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 rotatablymounted on a carrier member 39 and disposed in meshing relationship withboth the ring gear member 34 and the sun gear member 32.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The input member 17 is continuously connected with the sun gear member22 of the planetary gear set 20. The output member 19 is continuouslyconnected with the ring gear member 44 of the planetary gear set 40. Theplanet carrier assembly member 26 is continuously connected with thetransmission housing 60.

A first interconnecting member 70 continuously connects the sun gearmember 32 of the planetary gear set 30 with the sun gear member 42 ofthe planetary gear set 40. A second interconnecting member 72continuously connects the planet carrier assembly member 36 of theplanetary gear set 30 with the planet carrier assembly member 46 of theplanetary gear set 40.

The planetary gear arrangement also includes six torque-transmittingdevices 50, 52, 54, 55, 56 and 57. The torque-transmitting devices 50and 52 are stationary-type torque-transmitting devices, commonly termedbrakes or reaction clutches. The torque-transmitting devices 54, 55, 56and 57 are rotating-type torque-transmitting devices, commonly termedclutches.

A first torque-transmitting device, such a brake 50, selectivelyconnects the sun gear member 32 of the planetary gear set and the sungear member 42 of the planetary gear set 40 via interconnecting member70 with the transmission housing 60, and with the planet carrierassembly member 26 of the planetary gear set 20. A secondtorque-transmitting device, such as brake 52, selectively connects theplanet carrier assembly member 36 of the planetary gear set 30 and theplanet carrier assembly member 46 of the planetary gear set 40 viainterconnecting member 72 with the transmission housing 60. A thirdtorque-transmitting device, such as clutch 54, selectively connects thesun gear member 22 of the planetary gear set 20 with the sun gear member32 of the planetary gear set 30 and the sun gear member 42 of theplanetary gear set 40 via interconnecting member 70. A fourthtorque-transmitting device, such as clutch 55, selectively connects thesun gear member 22 of the planetary gear set 20 with the planet carrierassembly member 36 of the planetary gear set 30 and the planet carrierassembly member 46 of the planetary gear set 40 via interconnectingmember 72. A fifth torque-transmitting device, such as clutch 56,selectively connects the ring gear member 24 of the planetary gear set20 with the ring gear member 34 of the planetary gear set 30. A sixthtorque-transmitting device, such as clutch 57, selectively connects thering gear member 24 of the planetary gear set 20 with the sun gearmember 32 of the planetary gear set 30 and the sun gear member 42 of theplanetary gear set 40 via interconnecting member 70.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting devices are selectively engaged incombinations of two to provide at least eight forward speed ratios andat least one reverse speed ratio, all with single transition sequentialshifts, and including two overdrive ratios.

As set forth above, the engagement schedule for the torque-transmittingdevices is shown in the truth table of FIG. 1 b. The chart of FIG. 1 bdescribes the gear ratios and ratio steps that are attained in the abovedescribed transmission. For example, the step ratio between the firstand second forward speed ratios is 1.70, while the step ratio betweenthe reverse speed ratio and first forward ratio is −0.65.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format. A lever diagram is aschematic representation of the components of a mechanical device suchas an automatic transmission. Each individual lever represents aplanetary gearset, wherein the three basic mechanical components of theplanetary gear are each represented by a node.

The powertrain 10 includes an input member 17 continuously connectedwith the engine 12, an output member 19 continuously connected with thefinal drive 16, a first planetary gear set 20A having three nodes: afirst node 22A, a second node 26A and a third node 24A; a secondplanetary gear set 30A having three nodes: a first node 32A, a secondnode 36A and a third node 34A; and a third planetary gear set 40A havingthree nodes: a first node 42A, a second node 46A and a third node 44A.

The input member 17 is continuously connected with the node 22A. Theoutput member 19 is continuously connected with node 44A. The node 26Ais continuously connected with the transmission housing 60.

The node 32A is continuously connected with the node 42A viainterconnecting member 70. The node 36A is continuously connected withthe node 46A via interconnecting member 72.

A first torque-transmitting device, such as brake 50, selectivelyconnects the nodes 32A and 42A and the transmission housing 60, and withnode 26A. A second torque-transmitting device, such as brake 52,selectively connects the nodes 36A and 46A with the transmission housing60. A third torque-transmitting device, such as clutch 54, selectivelyconnects the node 22A with the node 32A. A fourth torque-transmittingdevice, such as clutch 55, selectively connects the node 22A with thenodes 36A and 46A via interconnecting member 72. A fifthtorque-transmitting device, such as clutch 56, selectively connects thenode 24A with the node 34A. A sixth torque-transmitting device, such asclutch 57, selectively connects the node 24A with the node 32A.

To establish ratios, two torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row. For example, to establish reversegear, the brake 52 and clutch 54 are engaged. The brake 52 engages thenodes 36A and 46A with the transmission housing 60. The clutch 54engages the node 22A with the node 32A. Likewise, the eight forwardratios are achieved through different combinations of clutch engagementas per FIG. 1 c.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having first,second and third members; a first interconnecting member continuouslyconnecting said first member of said second planetary gear set with saidfirst member of said third planetary gear set; a second interconnectingmember continuously connecting said second member of said secondplanetary gear set with said second member of said third planetary gearset; said second member of said first planetary gear set beingcontinuously connected with a stationary member; six torque-transmittingdevices each operable to selectively interconnect a respective one ofsaid members of said planetary gear sets with said stationary member, orwith another respective one of said members of said planetary gear sets,said six torque-transmitting devices being engaged in combinations oftwo to establish at least eight forward speed ratios and at least onereverse speed ratio between said input member and said output member;wherein a first of said six torque-transmitting devices is operable forselectively connecting said first member of said second planetary gearset with said stationary member; and wherein a second of said sixtorque-transmitting devices is operable for selectively connecting saidsecond member of said second planetary gear set with said stationarymember.
 2. The transmission of claim 1, wherein a third of said sixtorque-transmitting devices is operable for selectively connecting saidfirst member of said first planetary gear set with said first member ofsaid second planetary gear set.
 3. The transmission of claim 2, whereina fourth of said six torque-transmitting devices is operable forselectively connecting said first member of said first planetary gearset with said second member of said second planetary gear set.
 4. Thetransmission of claim 3, wherein a fifth of said six torque-transmittingdevices is operable for selectively connecting said third member of saidfirst planetary gear set with said third member of said second planetarygear set.
 5. The transmission of claim 4, wherein a sixth of said sixtorque-transmitting devices is operable for selectively connecting saidthird member of said first planetary gear set with said first member ofsaid second planetary gear set.
 6. The transmission of claim 1, whereintwo of said six torque-transmitting devices comprise brakes, and four ofsaid six torque-transmitting devices comprise clutches.
 7. Thetransmission of claim 1, wherein said first, second and third members ofsaid first, second and third planetary gear sets comprise a sun gearmember, a planet carrier assembly member and a ring gear member,respectively.
 8. The transmission of claim 1, wherein said input memberis continuously interconnected with said first member of said firstplanetary gear set; and said output member is continuouslyinterconnected with said third member of said third planetary gear set.9. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having first,second and third members; said input member being continuouslyinterconnected with said first member of said first planetary gear set;and said output member being continuously interconnected with said thirdmember of said third planetary gear set; said second member of saidfirst planetary gear set being continuously connected with a stationarymember; a first interconnecting member continuously connecting saidfirst member of said second planetary gear set with said first member ofsaid third planetary gear set; a second interconnecting membercontinuously connecting said second member of said second planetary gearset with said second member of said third planetary gear set; a firsttorque-transmitting device selectively connecting said first member ofsaid second planetary gear set with said stationary member; a secondtorque-transmitting device selectively connecting said second member ofsaid second planetary gear set with said stationary member; a thirdtorque-transmitting device selectively connecting said first member ofsaid first planetary gear set with said first member of said secondplanetary gear set; a fourth torque-transmitting device selectivelyconnecting said first member of said first planetary gear set with saidsecond member of said second planetary gear set; a fifthtorque-transmitting device selectively connecting said third member ofsaid first planetary gear set with said third member of said secondplanetary gear set; a sixth torque-transmitting device selectivelyconnecting said third member of said first planetary gear set with saidfirst member of said second planetary gear set; said torque-transmittingdevices being engaged in combinations of two to establish at least eightforward speed ratios and at least one reverse speed ratio between saidinput member and said output member.
 10. A multi-speed transmissioncomprising: an input member; an output member; first, second and thirdplanetary gear sets each having a sun gear member, planet carrierassembly member and ring gear member; said input member beingcontinuously interconnected with said sun gear member of said firstplanetary gear set; and said output member being continuouslyinterconnected with said ring gear member of said third planetary gearset; said planet carrier assembly member of said first planetary gearset being continuously connected with a stationary member; a firstinterconnecting member continuously connecting said sun gear member ofsaid second planetary gear set with said sun gear member of said thirdplanetary gear set; a second interconnecting member continuouslyconnecting said planet carrier assembly member of said second planetarygear set with said planet carrier assembly member of said thirdplanetary gear set; a first torque-transmitting device selectivelyconnecting said sun gear member of said second planetary gear set withsaid stationary member; a second torque-transmitting device selectivelyconnecting said planet carrier assembly member of said second planetarygear set with said stationary member; a third torque-transmitting deviceselectively connecting said sun gear member of said first planetary gearset with said sun gear member of said second planetary gear set; afourth torque-transmitting device selectively connecting said sun gearmember of said first planetary gear set with said planet carrierassembly member of said second planetary gear set; a fifthtorque-transmitting device selectively connecting said ring gear memberof said first planetary gear set with said ring gear member of saidsecond planetary gear set; a sixth torque-transmitting deviceselectively connecting said ring gear member of said first planetarygear set with said sun gear member of said second planetary gear set;said torque-transmitting devices being engaged in combinations of two toestablish at least eight forward speed ratios and at least one reversespeed ratio between said input member and said output member.